Cervical mucus hostility is the inability of sperm to penetrate the cervical mucus.

The cervical mucus is a jelly-like substance produced by minute glands in the cervical canal. It changes in consistency and composition with the menstrual cycle. Just before ovulation and under the effect of the hormone estrogen it becomes very watery and copious to allow the sperm to swim through it. After ovulation and under the effect of progesterone, the mucus becomes thick and sticky, which renders it impenetrable to the sperm. Once the sperm are in the mucus, they can stay there for a few days. Thus the mucus acts as a sperm reservoir.

Problems with cervical mucus usually cause no symptoms and are detected by a Post Coital Test . Problems could arise because there is not enough mucus to allow sperm to swim through, the mucus contains antisperm antibodies or the sperm is abnormal or defective .

This problem can be treated effectively with intra uterine insemination.